The invention relates to the fuel injection systems of internal combustion engines. More particularly, the invention relates to fuel injection systems using electromagnetic injection valves that are controlled by injection control pulses. The duration or length of the control pulse determines the time of opening of the electromagnetic valves and thereby determines the amount of fuel fed to the engine, which varies for various operational conditions. The present invention is based on the recognition that the pressure difference across the orifice of the injection valve which influences the amount of fuel delivered is itself dependent on engine load. This is so because the induction tube pressure changes as a function of the load on the engine, i.e. depending on the position of the throttle valve. At relatively high loads, when the throttle valve is wide open, the induction tube pressure is substantially higher than is the case at low load and with a nearly closed throttle valve, where the induction tube pressure is a possibly high vacuum. Accordingly, the pressure gradient across the injection valve, i.e. the difference between the fuel pressure within the valve and the induction tube pressure, is reduced during conditions of high engine load and the engine thus receives relatively less fuel under such conditions. The fuel quantity may be reduced by as much as ten percent and more due to the above-described set of circumstances.